The potential of L. scoparium, K. robusta and P. radiata to mitigate N-losses in silvopastural systems

The Potential of Myrtaceae Species for the Phytomanagement of Treated Municipal Wastewater

The use of native plants in land application systems for treated municipal wastewater (TMW) can contribute to ecological restoration. However, research on the potential of native species to manage the nutrients and contaminants contained in TMW is scarce. At a 10-hectare field site irrigated with TMW at >4000 mm yr-1, we investigated the distribution of nutrients and trace elements in the soil-plant system, comparing the New Zealand native Myrtaceae species Leptosperum scoparium and Kunzea robusta with pasture. The results showed that plant growth did not correlate with TMW irrigation rates. L. scoparium and K. robusta had higher foliar trace element concentrations than pasture, but these were not correlated with TMW irrigation rates. The pasture accumulated more N and P (68 kg of N ha-1 yr-1 and 11 kg of P ha-1 yr-1) than the Myrtaceae species (0.6-17 kg of N ha-1 yr-1 and 0.06-1.8 kg of P ha-1 yr-1). Regular harvesting of the pasture would likely remove more N and P from the site than the Myrtaceae species. The results highlight the importance of adjusting TMW application rates to the soil-plant capacity, in which case, native plants could provide ecological or economic value to TMW-irrigated land.

Genetic Variation in Flowering Traits of Tasmanian Leptospermum scoparium and Association with Provenance Home Site Climatic Factors

Leptospermum scoparium is emerging as an economically important plant for the commercial production of mānuka honey and essential oils, both exhibiting unique antibacterial attributes. To support its domestication this is the first quantitative genetic study of variation for L. scoparium traits. It utilised plants from 200 open-pollinated families derived from 40 native populations, from across the species range in Tasmania, grown in a common garden field trial. The traits studied were survival, growth, and the flowering traits precocity, the timing of seasonal peak flowering, flowering duration, and flowering intensity. Significant genetic variation was evident at the population level for all traits studied and at the family level for three traits—growth, flowering precocity, and time to peak flowering. These three traits had moderate to high narrow-sense heritability estimates ranging from 0.27 to 0.69. For six of the traits studied, population differences were associated with climate attributes at the locations where seed was collected, suggesting adaptation to the local climate may have contributed to the observed population differentiation. Population level geographical trends suggest that genotypes to focus on for domestication originate from the eastern half of Tasmania for precociousness and the western half of Tasmania for earlier time to peak flowering and extended flowering duration.

The Potential for Temporary Stand-Off Pads Integrated With Poplar and Willow Silvopastoral Systems for Managing Nitrogen Leaching

Intensive pastoral farming has been linked to adverse environmental effects such as soil degradation and increased fluxes of nitrogen, phosphorus, sediments, and pathogens into waterways, resulting in their degradation. Stand-off pads are engineered structures covered with bedding materials, available for occupation by stock to minimise those adverse effects to soil and water bodies. Wood chips are ideal for bedding due to their low cost, high water holding capacity, and stock preference as resting areas. While they reduce the mobility of both nutrients and pathogens, their effectiveness depends on the type of wood, size of the chips, pH, pad design, and feeding management used. Dissolved organic carbon, present in wood residue, may slow nitrogen mineralisation thereby decreasing loss via leachate. This effect depends on plant tannins and nutrients already stored within the plant tissue. Poplar and willow have high concentrations of tannins in leaves and bark with potential nitrification-inhibiting properties. When grown on-farm, these deep-rooted trees also reduce nitrogen leaching and prevent soil erosion. This review addresses the use of temporary stand-off pads within poplar or willow silvopastoral systems. Harvested trees can provide suitable wood chips for constructing the stand-off pad, while the deep rooting systems of the trees will reduce the moisture content of the pad, preventing waterlogging. A key objective is to discuss the feasibility and establishment of multiple temporary stand-off pads that allow for stock rotation from pad to pad, and subsequent on-site composting of wood-wastes into fertiliser, reducing both nutrient inputs and losses in agricultural systems. The review highlights the potential suitability of poplar and willow tree species for such a system.

Response of a Pioneering Species (Leptospermum scoparium J.R.Forst. & G.Forst.) to Heterogeneity in a Low-Fertility Soil

Root foraging may increase plant nutrient acquisition at the cost of reducing the total volume of soil explored, thereby reducing the chance of the roots encountering additional patches. Patches in soil seldom contain just one nutrient: the patch may also have distinct textural, hydrological, and toxicological characteristics. We sought to determine the characteristics of root foraging by a pioneering species, Leptospermum scoparium, using pot trials and rhizobox experiments with patches of biosolids. The growth of L. scoparium was increased by <50 t/ha equiv. of biosolids but higher doses were inhibitory. Roots foraged patches of biosolids in a low-fertility soil. There was no evidence of chemotaxis, rather, the roots proliferated toward the patch of biosolids, following chemical gradients of nitrate. While the biosolids also contained high concentrations of other nutrients (P, K, and S), only significant chemical gradients of nitrate were found. Once the roots encountered a patch of biosolids, the growth of the plant increased to a level similar to plants growing in soil homogeneously mixed with biosolids or surface-applied biosolids. Our results indicate that roots forage nitrate, which is mobile in soil, and that gradients of nitrate may lead to patches containing other less mobile nutrients, such as phosphate or potassium.